1. Field of the Invention
The present invention relates to a system and method for controlling an automatic transmission in a vehicle.
2. Background Art
Automatic transmissions have long offered a number of manual gears that can be selected by the vehicle operator when driving conditions so dictate. For example, when driving on a steep incline, the driver may wish to manually downshift the automatic transmission into a lower gear to reduce the amount of pedal braking necessary to keep the vehicle at a moderate speed. In addition, a large vehicle, or one that hauls or tows heavy cargo, may benefit from the use of manually selected gears even when the vehicle is not on a steep incline. For example, the braking force required to stop a heavy vehicle, or a vehicle that hauls or tows heavy cargo, may be high enough to quickly wear brake pads if pedal braking is used exclusively. Thus, it may be beneficial to manually downshift to employ some engine braking even on relatively level road surfaces.
Although professional truck drivers are familiar with the use of downshifting to provide engine braking to slow a vehicle, the average passenger car driver may not be. Despite the availability of manually selectable low gears on most automatic transmissions, an average passenger car driver may not take advantage of them. Thus, it is desirable to provide a system and method for controlling an automatic transmission, such that the transmission is automatically downshifted into a lower gear when it is determined that engine braking is desired. Moreover, it may be beneficial to increase the speed at which the transmission automatically upshifts to a higher gear, so that the transmission remains in a lower gear for a longer period of time. The lower gear can provide additional torque that may be beneficial when towing or hauling heavy cargo. Some large vehicles, such as motor homes, currently employ the use of automatic transmissions that automatically downshift to help slow the vehicle when the driver applies the brakes when descending long, steep grades. However, a need still exists for a system and method for controlling an automatic transmission that will provide automatic downshifting when the brake pedal is not engaged, and that can determine when and how to automatically downshift based on one or more vehicle conditions.